Angular momentum transport efficiency in post-main sequence low-mass stars

Spada, F.; Gellert, M.; Arlt, R.; Deheuvels, S.

doi:10.1051/0004-6361/201527591

Cited by 75 publications

(112 citation statements)

References 57 publications

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“…The asteroseismic data obtained for the stellar core rotation from the mixed modes stochastically excited in sub-giants and red giants provide very good constraints for the transport of angular momentum in evolved stars (e.g. Beck et al 2012;Mosser et al 2012;Deheuvels et al 2012Deheuvels et al , 2014Deheuvels et al , 2015Spada et al 2016;Gehan et al 2018). The observed stars have masses ranging between 1.1 and 1.4 M .…”

Section: Case Of Red Giant Stars Illustrated With a 125 M Modelmentioning

confidence: 99%

Anisotropic turbulent transport in stably stratified rotating stellar radiation zones

Mathis

Prat

Amard

et al. 2018

A&A

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Context. Rotation is one of the key physical mechanisms that deeply impact the evolution of stars. Helio-and asteroseismology reveal a strong extraction of angular momentum from stellar radiation zones over the whole Hertzsprung-Russell diagram. Aims. Turbulent transport in differentially rotating stably stratified stellar radiation zones should be carefully modeled and its strength evaluated. Stratification and rotation imply that this turbulent transport is anisotropic. Only phenomenological prescriptions have been proposed for the transport in the horizontal direction, which however constitutes a cornerstone in current theoretical formalisms for stellar hydrodynamics in evolution codes. We aim at improving its modeling. Methods. We derive a new theoretical prescription for the anisotropy of the turbulent transport in radiation zones using a spectral formalism for turbulence that takes simultaneously stable stratification, rotation, and a radial shear into account. Then, the horizontal turbulent transport resulting from 3D turbulent motions sustained by the instability of the radial differential rotation is derived. We implement this framework in the stellar evolution code STAREVOL and quantify its impact on the rotational and structural evolution of solar metallicity low-mass stars from the pre-main-sequence to the red giant branch. Results. The anisotropy of the turbulent transport scales as N 4 τ 2 / 2Ω 2 , N and Ω being the buoyancy and rotation frequencies respectively and τ a time characterizing the source of turbulence. This leads to a horizontal turbulent transport of similar strength in average that those obtained with previously proposed prescriptions even if it can be locally larger below the convective envelope. Hence the models computed with the new formalism still build up too steep internal rotation gradients compared to helioseismic and asteroseismic constraints. As a consequence, a complementary transport mechanism like internal gravity waves or magnetic fields is still needed to explain the observed strong transport of angular momentum along stellar evolution. Conclusions. The new prescription links for the first time the anisotropy of the turbulent transport in radiation zones to their stratification and rotation. This constitutes an important theoretical progress and demonstrates how turbulent closure models should be improved to get firm conclusions on the potential importance of other processes that transport angular momentum and chemicals inside stars along their evolution.

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Section: Case Of Red Giant Stars Illustrated With a 125 M Modelmentioning

confidence: 99%

Anisotropic turbulent transport in stably stratified rotating stellar radiation zones

Mathis

Prat

Amard

et al. 2018

A&A

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“…The combination of space-based helio-and asteroseismology has demonstrated that stably stratified rotating stellar radiation zones are the seats of efficient transport of angular momentum throughout the evolution of stars. This strong transport leads to a uniform rotation in the case of the Sun down to 0.2 R (García et al 2007) and to weak differential rotation in other stars (e.g., Mosser et al 2012;Deheuvels et al 2012Deheuvels et al , 2014Kurtz et al 2014;Saio et al 2015;Murphy et al 2016;Spada et al 2016;Van Reeth et al 2016Aerts et al 2017;Gehan et al 2018;Ouazzani et al 2019). Four main mechanisms that transport angular momentum and mix chemicals are present in stellar radiation zones (e.g., Maeder 2009;Mathis 2013;Aerts et al 2019, and references therein): instabilities of the differential rotation (e.g., Zahn 1983Zahn , 1992, stable and unstable magnetic fields (e.g., Spruit 1999;Fuller et al 2019), internal gravity waves (e.g., Zahn et al 1997;Talon & Charbonnel 2005;Pinçon et al 2017), and largescale meridional circulations (e.g., Zahn 1992;Maeder & Zahn 1998;.…”

Section: Introductionmentioning

confidence: 99%

Horizontal shear instabilities in rotating stellar radiation zones

Park

Prat

Mathis

2020

A&A

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Context. Stellar interiors are the seat of efficient transport of angular momentum all along with their evolution. In this context, understanding the dependence of the turbulent transport triggered by the instabilities of the vertical and horizontal shears of the differential rotation in stellar radiation zones as a function of their rotation, stratification, and thermal diffusivity is mandatory. Indeed, it constitutes one of the cornerstones of the rotational transport and mixing theory which is implemented in stellar evolution codes to predict the rotational and chemical evolutions of stars. Aims. We investigate horizontal shear instabilities in rotating stellar radiation zones by considering the full Coriolis acceleration with both the dimensionless horizontal Coriolis componentf and the vertical component f . Methods. We performed a linear stability analysis using linearized equations derived from the Navier-Stokes and heat transport equations in the rotating non-traditional f -plane. We considered a horizontal shear flow with a hyperbolic tangent profile as the base flow. The linear stability was analyzed numerically in wide ranges of parameters, and we performed an asymptotic analysis for large vertical wavenumbers using the Wentzel-Kramers-Brillouin-Jeffreys (WKBJ) approximation for non-diffusive and highly diffusive fluids. Results. As in the traditional f -plane approximation, we identify two types of instabilities: the inflectional and inertial instabilities. The inflectional instability is destabilized asf increases and its maximum growth rate increases significantly, while the thermal diffusivity stabilizes the inflectional instability similarly to the traditional case. The inertial instability is also strongly affected; for instance, the inertially unstable regime is also extended in the non-diffusive limit as 0 < f < 1 +f 2 /N 2 , where N is the dimensionless Brunt-Väisälä frequency. More strikingly, in the high-thermal-diffusivity limit, it is always inertially unstable at any colatitude θ except at the poles (i.e., 0 • < θ < 180 • ). We also derived the critical Reynolds numbers for the inertial instability using the asymptotic dispersion relations obtained from the WKBJ analysis. Using the asymptotic and numerical results, we propose a prescription for the effective turbulent viscosities induced by the inertial and inflectional instabilities that can be possibly used in stellar evolution models. The characteristic time of this turbulence is short enough so that it is efficient to redistribute angular momentum and mix chemicals in stellar radiation zones.

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“…The authors found a ν add of 3 × 10 4 cm 2 s −1 as a mean value for the efficiency of the transport process, constrained strongly by the asteroseismic observations. Spada et al (2016) followed a similar approach to constrain the missing process by including a diffusive process to the transport of angular momentum that varies with the ratio of core to envelope rotation rate, inspired by the azimuthal magneto-rotational instability (AMRI, see Rüdiger et al 2007). They compare their stellar evolution models to observations of core rotation rate from Deheuvels et al (2014) and Mosser et al (2012) and conclude that the missing process of angular momentum transport has to change throughout the evolution of a star to be able to match the post-main sequence rotational evolution of lowmass stars.…”

Section: Introductionmentioning

confidence: 99%

Constraining transport of angular momentum in stars

Hartogh

Eggenberger

Hirschi

2019

A&A

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Context. Transport of angular momentum has been a challenging topic within the stellar evolution community, even more since the recent asteroseismic surveys. All published studies on rotation using asteroseismic observations show a discrepancy between the observed and calculated rotation rates, indicating there is an undetermined process of angular momentum transport active in these stars. Aims. We aim to constrain the efficiency of this process by investigating rotation rates of 2.5 M stars. Methods. First, we investigated whether the Tayler-Spruit dynamo could be responsible for the extra transport of angular momentum for stars with an initial mass of 2.5 M . Then, by computing rotating models including a constant additional artificial viscosity, we determined the efficiency of the missing process of angular momentum transport by comparing the models to the asteroseismic observations of core helium burning stars. Parameter studies were performed to investigate the effect of the stellar evolution code used, initial mass, and evolutionary stage. We evolved our models into the white dwarf phase, and provide a comparison to white dwarf rotation rates. Results. The Tayler-Spruit dynamo is unable to provide enough transport of angular momentum to reach the observed values of the core helium burning stars investigated in this paper. We find that a value for the additional artificial viscosity ν add around 10 7 cm 2 s −1 provides enough transport of angular momentum. However, the rotational period of these models is too high in the white dwarf phase to match the white dwarf observations. From this comparison we infer that the efficiency of the missing process must decrease during the core helium burning phase. When excluding the ν add during core helium burning phase, we can match the rotational periods of both the core helium burning stars and white dwarfs.

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Angular momentum transport efficiency in post-main sequence low-mass stars

Cited by 75 publications

References 57 publications

Anisotropic turbulent transport in stably stratified rotating stellar radiation zones

Anisotropic turbulent transport in stably stratified rotating stellar radiation zones

Horizontal shear instabilities in rotating stellar radiation zones

Constraining transport of angular momentum in stars

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